1. Field of the Invention
Current methods used in infectious disease diagnosis usually involve detection of bacterial products, particularly genetic products. These may be enzymes detected by biochemical methods or surface structures or other protein or in some instances carbohydrate substances detected immunologically. In many cases these tests are feasible only if sufficient numbers of living microorganisms are present. Other problems are also frequently encountered.
One of the problems encountered in present day diagnosis can be illustrated by diarrheal illness resulting from enterotoxigenic E. coli. One impediment to the diagnosis is the difficulty in differentiating toxin-producing E. coli from the harmless E. coli ordinarily found in the bowel of human or animals. Current methods to detect toxin-producing E. coli involve the detection of the toxin itself by biological and immunological assays. One form of toxin (heat labile toxin-LT) is detected by tissue culture or immunological assays. Another form of E. coli toxin (heat stable toxin-ST) is assayed in animals and involves sacrificing the animals and examining fluid accumulation in the gut. These techniques require manipulation of individual clinical isolates. Current screening for toxigenic E. coli is costly, inconvenient, and time consuming. This technique in one of its embodiments can get around that problem.
It would therefore be of great value to provide a simple and rapid screening capability which would allow for rapid simultaneous testing of large numbers of samples with a high degree of reliability. For commercial applications, it is desirable to have preprepared kits containing reagents which are standardized and optimized for sensitivity and accuracy.
2. Description of the Prior Art
Present methods for detecting the presence of enterotoxigenic E. coli may be found in Dean et al. J. Infect. Dis. 125:407-411, 1972; Guerrant et al., Infect. Immun. 10:310-327, 1974; Sack and Sack, ibid. 11:334-336, 1975; Volken et al. J. Clin. Microbiol. 6:439-444, 1977; Evans et al. Infect. Immun. 7:873-880, 1973; and Smith and Gyles, J. Med. Microbiol. 3:403-409, 1970. The genes and coding for the LT and ST have been isolated and described by Dallas et al., J. Bacteriol. 139:850-858, 1979, and So et al. Nature 277:453-456, 1979. The method of colony hybridization for isolation of cloned organisms having a specific gene is described by Grunstein and Hogness, Proc. Nat. Acad. Sci. USA. 72:3961-3965, 1975.